This invention relates to the field of surface catalytic reactions and/or heat exchange. The present invention provides a reactor which fits within a cylindrical outer tube, and which effectively transfers heat from the exterior of the outer tube to the reactor, or from the reactor to the outer tube.
The reactor of the present invention achieves the same objectives as those of the catalyst supports described in copending U.S. patent application Ser. No. 11/132,691, filed May 19, 2005, Ser. No. 10/896,302, filed Jul. 21, 2004, and Ser. No. 11/105,973, filed Apr. 14, 2005. The disclosures of the above-mentioned applications are incorporated by reference herein.
One of the objectives of the reactors described in the above-cited applications is to avoid the problems associated with the use of ceramic materials in the manufacture and operation of catalytic reactors. Packed bed ceramic catalysts have the disadvantage that they have low thermal conductivity, making it difficult to transfer heat from the periphery of the reactor to the inside, or vice versa. Also, the thermal mismatch between the metal and ceramic portions of prior art reactors eventually leads to pulverization of the ceramic material, thus limiting the useful life of the reactor. Like the devices described in the above-cited applications, the present invention also comprises an all-metal structure which inherently avoids these problems.
A reactor having radial leaves, as described in application Ser. No. 11/132,691, has shown good heat transfer, and therefore good overall performance, not only when simulated in a computer model, but also when evaluated as a prototype in a heat transfer rig. However, the prototype has proved quite difficult to build, and is not believed to be an optimum solution, from the standpoint of ease of manufacture.
The reactors shown in the above-cited applications, and others reactors of the prior art, occupy substantially all of the space within a cylindrical outer tube. An inherent problem with reactors of this kind is that they do not perform particularly well near the center of the reactor. It has been found that most of the catalytic reactions occur near the outer portions of the reactor, i.e. near the outer tube. This problem reduces the efficiency of the reactor, and makes it very difficult or impossible to achieve the desired level of conversion.
The present invention provides a reactor structure which solves the above problem. The reactor of the present invention is substantially more efficient than reactors of the prior art, and is also relatively easy to manufacture.
Another problem encountered with reactors installed in cylindrical tubes is that of metallic creep. The reactors described in the above-cited applications, as well as the reactor of the present invention, are intended to be stuffed into a large metallic outer tube and operated at high temperatures (in the range of 850-900° C.) and high pressures (in the range of 20-30 bar). The pressure creates a large hoop stress, which the tube material has difficulty resisting at the high temperature. Over a period of years, creep in the metal outer tube causes the diameter of the tube to grow. Even a few millimeters of growth in the tube diameter creates an undesirable gap between the reactor and the surrounding tube. A typical reactor which has been stuffed into a new tube, such that the reactor is initially in good contact with the tube, will lose contact with the tube when the tube creeps over the years. Such creep will cause a significant drop in performance.
The present invention provides structure which avoids the above problem. The invention includes a device that continuously compensates for creep, insuring proper contact between the reactor and the surrounding outer tube.
The reactor of the present invention can be used, for example, in the field of catalytic fuel reforming, to make hydrogen, which is then used to generate electricity through a fuel cell, or in other industrial processes such as oil and gas refining, ammonia and fertilizer production, hydrogenation of oils and chemicals, and iron ore reduction. The reactor could be used as a catalytic or non-catalytic combustor, or as a simple heat exchanger.